Flavylium compound

Photochrome flavylium compounds as multistate/multifunction molecular-level systems 99CC107. 

Each anthocyanidin is involved in a series of equilibria giving rise to different forms, which exhibit their own properties including color. One- and two-dimensional NMR have been used to characterize the various forms of malvidin 3,5-diglucoside present in aqueous solution in the pH range 0.3 to 4.5 and to determine their molar fractions as a function of pH. In addition to the flavylium cation, two hemiacetal forms and both the cis and trans forms of chalcone were firmly identified. In a reexamination, the intricate pH-dependent set of chemical reactions involving synthetic flavylium compounds (e.g., 4 -hydroxyflavylium) was confirmed to be basically identical to those of natural anthocyanins (e.g., malvidin 3,5-diglucoside) in... 

Pina, F., Maestri, M., and Balzani, V., Photochromic systems based on synthetic flavylium compounds and their potential use as molecular-level memory elements, in Handbook of Photochemistry and Photobiology, Abdel-Mottaleb, M.S.A. and Nalwa, H.S.Eds., American Scientific Publishers, Stevenson Ranch, 2003, 3, 411. 

Multistate/Multifunctional Molecular-level Systems-Photochromic Flavylium Compounds... 

In this chapter, we discuss the multistate/multifunctional character of the chemistry of synthetic photochromic flavylium compounds and show that the examination of complex chemical systems from novel viewpoints may reveal very interesting features and may be useful to introduce new concepts in the field of chemical... 

In flavylium compounds that bear OH substituents in their 4 - and/or 7-positions, deprotonation of the OH group can result in other forms being obtained, not seen in the case of the 4 -methoxyflavylium compound discussed above. Figure 8 illustrates this for the 4 -hydroxyflavylium ion.1171 The new species are the quinoidal base A, obtained by simple deprotonation of the AH+ flavylium cation, and the dianionic Cc2- and Ct2- forms, obtained by second deprotonations of Cc and Ct. The roles played by these forms depend on the specific compound and the pH conditions. For... 

As discussed above for the 4,-methoxyflavylium compound, pH jump, temperature jump, and flash photolysis experiments permit the measurement of the rate constants of some of the reactions involved, while steady state titration experiments (using UV-Vis and NMR techniques) enable equilibrium constants to be determined. The values obtained for the most important processes in five flavylium compounds are gathered in Table 1. 

Tab. 1 Thermodynamic and kinetic constants for some structural transformations of synthetic flavylium compounds.3...

Fig. 14 Hydraulic analogy for the description of the behavior of flavylium compounds upon a pH-jump from pH = 1.0 to pH = 4.0.[411.

Fig. 15 Hydraulic analogy for the photochemical reaction of the Ct form of the flavylium compounds. Light behaves like a pump that increases (in a transient mode as represented, or in a steady state) the quantity of liquid in the reservoir Cc.

Synthetic flavylium compounds can exist in several forms (multistate), which can be interconverted by more than one type of external stimulus (multifunctional). The intricate network made up by their reactions, when examined from the viewpoints of molecular level devices and molecular level logic functions , reveals that these systems exhibit very interesting properties. 

NMR spectroscopy of flavan-3-ols and proantocyanidines 97KPS545. Photochrome flavylium compounds as multistate/multifunction molecular-level systems 99CC107. 

The photochromic behaviour of synthetic flavylium compounds, more properly the one of the trans-chalcone spiecies, only recently was perceived as a new photochromic system with many p>otentiahties.[7] In spite of its ap>p)arent complexity is a simple sequence of three well known elementary steps i) photo induced isomerisation ii) cyclization and iii) dehydration to give the coloured product, the flavylium cation, (or the very coloured quinoidal base, depending on pH), Scheme 2.7. 

The network of flavylium compounds in water (acid to moderately acid) is easily accounted for by eq.(l) to eq.(4)[8,9]... 

Flavylium compound with cis-trans isomerisation thermal barrier... 

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